The present invention relates to up converters designed for use in the headend of a cable television distribution system and more particularly to an agile output band pass filter circuit for use in conjunction with an agile up converter, which enables the system operator use a single output filter circuit for all channels.
In the headend of a cable television distribution system, video programs are prepared for distribution by modulating a carrier of a frequency corresponding to the channel selected. This is accomplished by means of a video modulator and an up converter. The video modulator converts the video signal to an intermediate (IF) frequency signal. The up converter converts the IF signal to a signal at the selected channel frequency.
Up converters which can be programmed for use for any one of the eighty-six available channels per cable are known as "agile". The last portion in an up converter is an output filter which prevents unwanted frequencies from being coupled to the cable distribution system. Even with an agile up converter, a different dedicated output filter is needed for each channel selected because different channel frequencies require filters with different pass bands to successfully minimize spurious output and broadband noise. Hence, the system operator must physically change the output filter each time the up converter is set to a different channel frequency.